1. Field of the Invention
This invention relates to a microscope and, in particular, to an infrared microscope in which a visual observation can be made, and an observation tube used for this microscope.
2. Description of Related Art
Recently, an infrared microscope utilizing light in a near-infrared region has been used for the FCB inspection of the silicon substrate of a semiconductor and in a Raman spectroscope.
In an infrared observation under a conventional infrared microscope, infrared light with wavelengths up to 1300 nm has been generally used.
The conventional infrared microscope includes a light source which is capable of emitting infrared light with wavelengths up to about 1300 nm, for example, a halogen lamp which has high luminance in an infrared region, an illumination optical system for illuminating a specimen, an infinite objective lens in which aberration is corrected with respect to light ranging from a visible region to the infrared region (1300 nm), forming an image of the specimen, and a lens for forming an image of light from the objective lens. Moreover, the microscope has a visual observation optical path for making a visual observation of the specimen, an infrared observation optical path for making an infrared observation through a TV camera, provided to be independent of the visual observation optical path, a path switching prism for switching an optical path to one of the above two optical paths to introduce the light from the objective lens thereinto, and an eyepiece in which aberration is favorably corrected with respect to only light in the visible region.
The path switching prism is coated with a reflecting coating for reflecting all of light and is placed to be movable in and out of the optical path from the objective lens, or is half-coated so that light can be separated and introduce into the visual observation optical path and the infrared observation optical path at any ratio to carry out the infrared observation and the visual observation at the same time, and is disposed in the optical path from the objective lens.
An observation tube used in this infrared microscope includes an imaging lens for conducting the light from the objective lens and the path switching prism, having the visual observation optical path and the infrared observation optical path.
In such a conventional infrared microscope, when the path switching prism is disposed so that emergent light follows the visual observation optical path, the path switching prism reflects even near-infrared light (visible infrared light) which irradiates the specimen and is then reflected to pass through the objective lens, together with visible light, and introduces the light into the visual observation optical path. Consequently, an observer will carry out a visual observation of an image with visible light containing infrared light.
In the visual observation, however, an eyepiece is not favorably corrected for aberration with respect to near-infrared light, and thus the view of an image is impaired because of aberration produced by near-infrared light in a visible wavelength region. That is, the human eye is sensitive to light with wavelengths up to, 750-800 nm, depending on the individual.
However, since the wavelength region in which the eyepiece is favorably corrected for aberration is up to 700 nm and light with longer wavelengths yields aberration, the view of the image is impaired.
Furthermore, since the infrared observation is carried out by relatively increasing the intensity of light on the long-wavelength side, red light on the long-wavelength side becomes more intense than blue-purple light on the short-wavelength side, and an image under the visual observation has a reddish, unnatural hue, as a whole.
Thus, in order to eliminate the unfavorable view and the unnatural hue of the image of the visual observation, an element for blocking infrared light, for example, an IR cut-off filter or a color temperature compensating filter, is placed in the optical path of the illumination optical system only in the case of the visual observation. By doing so, infrared light with long wavelengths more than 700 nm, which is responsible for aberration due to infrared light and the unnatural hue of the image due to a large amount of light with long wavelengths, is blocked by the filter, and hence a favorable image can be obtained.
In this case, however, the problem arises that infrared light with wavelengths of 800-1300 nm required for the infrared observation is also blocked by the element for blocking infrared light and the specimen is not irradiated with infrared light. Therefore, when the infrared observation is carried out, the element for blocking infrared light must be removed from the optical path of an illumination system. This causes inconvenience to the operation of the microscope. Specifically, in the conventional infrared microscope, the specimen is irradiated with infrared light to observe the image of the specimen with the infrared light through a TV camera, and thus the element for blocking infrared light necessary for the observation cannot be fixed and placed in the optical path between the light source and the light-receiving surface of the TV camera. Moreover, when the infrared observation is carried out through the TV camera, aberration of light with longer wavelengths than the wavelength at which the objective lens is favorably corrected for aberration is produced, and light with wavelength at which the objective lens is not corrected for aberration is also received by the TV camera. This deteriorates the view of the image.
It is, therefore, an object of the present invention to provide an infrared microscope in which aberration due to infrared light is favorably corrected and an image which has no unnatural hue due to a large amount of light with long wavelengths can be obtained without moving the element for blocking infrared light in a visual observation, and an observation tube used for this microscope.
In order to achieve this object, the infrared microscope according to the present invention includes a light source emitting infrared light, an objective optical system for forming an image of a specimen, a first optical path for carrying out a visual observation of the image of the specimen, a second optical path provided to be independent of the first optical path, a path switching member located at a position where the first optical path intersects with the second optical path, a driving mechanism for moving the path switching member, and an infrared-light blocking member placed in the first optical path.
The observation tube used for the infrared microscope according to the present invention includes a first optical path for carrying out a visual observation of an image of a specimen formed by an objective optical system, a second optical path provided to be independent of the first optical path, a path switching member located at the position where the first optical path intersects with the second optical path, a driving mechanism for moving the path switching member, and an infrared-light blocking member placed in the first optical path.
According to the present invention, the first optical path is provided with an eyepiece.
According to the infrared microscope of the present invention, an image which is free of aberration due to infrared light and has no unnatural hue due to a large amount of light with long wavelengths can be obtained without moving the element for blocking the infrared light in a visual observation. Furthermore, even in the infrared observation, an image which is free of aberration can be obtained with respect to light with longer wavelengths than the wavelength at which the objective lens is corrected for aberration, and a favorable observation can be always carried out.
This and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.